Witnesses said the tail hit the ground first and broke off, and the jet spun out of control. Flight 214 had 291 passengers and 15 crew members, of whom 181 were taken to hospitals, San Francisco Assistant Deputy Fire Chief Dale Carnes told reporters today. One person was unaccounted for, Carnes said.

The plane, Boeing’s largest twin-engine model, appears to have struck a seawall where the runway meets San Francisco Bay, said John Cox, a Washington-based aviation safety consultant who has participated in several National Transportation Safety Board investigations. That suggests that the jet was coming in short of the runway, Cox said in an interview.

“It’s not a little bit short,” Cox said. “It’s a lot short.”

The NTSB said it was sending a team to investigate the accident, the most serious on U.S. soil since 50 people were killed on Feb. 12, 2009, near Buffalo, New York, when a turboprop plane flown by Pinnacle Airlines Corp.’s former Colgan unit plunged to the ground.

Five crash victims were in critical condition at San Francisco General Hospital, a spokeswoman, Rachael Kagan, told reporters.

Clear Skies

Weather didn’t immediately appear to have played a role in the crash, with visibility at the San Francisco airport at the time exceeding 10 miles (16 kilometers), a few clouds at 1,600 feet and winds from the southwest at 6 to 7 knots, according to FlightAware.com, an industry data compiler. Those conditions wouldn’t have had any effect on a 777 in normal operations.

Arriving flights had been operating under “visual flight rules,” said Doug Yakel, an airport spokesman. The glide slope indicator, a piece of the instrument landing system that assists pilots in landing in cloudy skies, wouldn’t have been in use, Yakel said.

Television pictures broadcast from San Francisco showed the airliner’s escape slides deployed and passengers running away on a sunny, clear afternoon. The top of the plane appeared burned away in places.

Two Strikes

A passenger named Lee told South Korean broadcaster YTN by telephone that as the plane was about to land, its nose was angled unusually high. The tail struck first, the jet bobbed upward from the impact, then crashed into the runway again. At the second impact, fire spread through the plane, the man said.

The passengers included 77 South Koreans, 141 Chinese, 61 from the U.S., and one Japanese person, according to a statement from Asiana.

“Just crash landed at SFO. Tail ripped off. Most everyone seems fine. I’m ok. Surreal,” he said in one post. “Fire and rescue people all over the place They’re evacuating the injured. Haven’t felt this way since 9/11.”

Inside the airport, about 50 passengers, family members and Red Cross workers were in the “reflection room” of the international terminal. Airport officials and police officers escorted them in and out and didn’t let them respond to questions. Two airport workers in bright yellow vests each carried in white garbage bags filled with snack chips. About 25 to 30 family members were awaiting word of victims’ condition.

Sandberg’s Switch

Sheryl Sandberg, chief operating officer of Facebook Inc (FB)., operator of the world’s biggest Internet social network, said on her page that she almost took the plane, but switched to another flight so as to use frequent-flier miles.

“Taking a minute to be thankful,” she wrote. “Thank you to everyone who is reaching out -- and sorry if we worried anyone.”

The 777 is among the most-popular long-haul jetliners, because it combines the fuel efficiency of a twin-engine model with the ability to carry more than 300 people, depending on the variant and the cabin configuration. Doug Alder, a spokesman for Boeing’s commercial aircraft business, said the Chicago-based planemaker will assist NTSB investigators.

Third Accident

The accident marked the third time a 777 was destroyed in an accident, according to AviationSafetyNetwork, an online log of aviation crashes. No one died in the two previous incidents.

A British Airways Plc 777 landed short of a runway at London’s Heathrow Airport on Jan. 17, 2008, after its engines stopped, according to the U.K.’s Air Accidents Investigation Branch. The plane came to rest in a field.

An EgyptAir 777 was destroyed by fire on the ground at Cairo International Airport on July 29, 2011, according to AviationSafetyNetwork. The fire erupted in the cockpit as the crew was preparing to depart.

The San Francisco airport was initially closed to all incoming and outgoing flights after the crash, though two of four runways were later reopened.

More than 300 flights were canceled as crews worked to clean up the wreckage and begin an investigation. The tally consisted of 195 departures and 148 inbound flights, according to FlightAware.

San Francisco is a hub for United Airlines, which reported the most scrubbed flights. A telephone message left for comment about the disruptions wasn’t immediately returned.